Hydrofluoroolefins (HFOs), such as tetrafluoropropenes, including 2,3,3,3-tetrafluoropropene (HFO-1234yf), are known to be effective refrigerants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. Unlike chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), both of which potentially damage the Earth's ozone layer, HFOs do not contain chlorine and thus pose no threat to the ozone layer. HFO-1234yf has also been shown to be a low global warming compound with low toxicity and, hence, can meet increasingly stringent requirements for refrigerants in mobile air conditioning. Accordingly, compositions containing HFO-1234yf are among the materials being developed for use in many of the aforementioned applications.
One manufacturing process for HFO-1234yf uses 1, 1, 2, 3-tetrachloropropene (1230xa) as starting raw material. The process comprises the following three steps:
Step (1): 1230xa+3HF→2-chloro-3,3,3,-trifluoropropene (1233xf)+3 HCl in a vapor phase reactor charged with a solid catalyst,
Step (2): 1233xf+HF→2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) in a liquid phase reactor charged with a liquid catalyst; and
Step (3): 244bb→1234yf+HCI in a vapor phase reactor.
In Step (2), the conversion of 1233xf is often incomplete, and some 1233xf is carried over to Step (3) along with 244bb. The presence of 1233xf in the Step (3) feed is undesired inasmuch as it renders various advantageous recycles problematic, and raises the potential for unwanted side reactions, among other things. Separating 1233xf from 244bb is thus preferred. U.S. Published Patent Application No. 2013/0085308 relates that activated carbon, used to separate 1233xf from 244bb, can be regenerated by heating, vacuum or an inert gas stream. Regenerating the activated carbon is economically important. Nonetheless, other methods of regenerating activated carbon, and of regenerating other adsorbents useful for separating 1233xf from 244bb, are desired.